Thomas a



(No Model.)

T. A. EDISON.

ELECTRODE FOR TELEPHONE TRANSMITTERS No. 348,114. 1 Patented Aug. 24,1886.

AT TEST INVENTOB:

N. vefca's mummm mr. Waxhingmn. n.'c.

NITED STATES ATENT FFICE THOMAS A. EDISON, OF MENLO PARK, NE\V JERSEY.

ELECTRODE F OR TELEPHO NE-TRANSMITTERS.

SPECIFICATION forming part of Letters Patent No. 348,114, dated August24, 1886,

Application filed Octobtr 14, 1885. Serial No. 179,800. (No model.)

To all whom it may concern:

Be it known that I, THoMAs A. EDIsoN, of Menlo Park, in the county ofMiddlesex and State of New Jersey, have invented a certain new anduseful Improvement in Electrodes for Telephone-Transmitters, of whichthe following is a specification.

This invention relates to the carbon electrodes or buttons fortelephone-transmitters; and its object is to increase the effectivenessin use of such electrodes.

The carbon button of my invention consists of a base of textile or wovenfabric (or of a certain equivalent material, hereinafterv described)whose meshes are filled or impregnated and whose surfaces are coveredwith lamp-black, plumbago, or carbon in any other suitable form. Thefabric may be fine wiregauze, or any material woven from animal orvegetable fiber. I prefer to use veiling or other cloth of a similartexture. A flat piece of the material chosen, of the proper size for thecarbon button, and usually of circular form, is laid upon a quantity ofthe powdered carbon, and more of the carbon is then placed upon the flatpiece. Pressure is then applied in any suitable manner to the carbon andfabric, and the carbon is thus forced into the meshes or interstices ofthe fabric and fills the same, so that the fabric is thoroughlyimpregnated with the carbon and is covered on each side with a layer ofcarbon. For some forms of carbon a suitable glutinous or sticky materialis employed to unite the carbon particles.

- IVith lamp-black, however, no such thing is required. I have foundthat carbon buttons of this character are more effective in use thanthose composed wholly of carbon, and I think the reason for this is thatat those parts of the button where the carbon lies upon the threads orwires of the fabric the surface is higher than at those parts where itis forced into the meshes between the threads, and therefore the surfaceof the button is provided with a great number of minute raised contactparts, whereby better contact is attained with the opposing surface thanwhere the button has a perfectly-flat surface.

I prefer the fabric of animal or vegetable fiber to the metal gauze,because the wires of the latter are smooth and slippery and do notretain the carbon upon their surfaces under pressure, like the threadsof the former.

Instead of the textile fabric I may employ a disk of thin paperperforated with a large number of small holes so thickly that itsstructure is similar to that of a woven fabric. This evidently may beconsidered the equivalent of the textile fabric. The carbon is pressedinto the apertures and remains upon the surface of the intermediatepaper in the same manner as above described.

The base of textile fabric, or its equivalent, holds the carbontogether, so that the whole forms an integral structure.

My invention is illustrated in the accompanying drawings, in whichFigure 1 represents a piece of animal or vegetable fabric for the baseof a carbon button; Fig. 2, a piece of wire-gauze for the same purpose;Fig. 3, a piece of perforated paper for the same purpose; Fig. 4, acomplete carbon button, and Fig. 5 is an exaggerated sectional view ofsuch carbon button.

A is a circular disk cut from apiece of veiling or similar fabric; B, adisk of wire-gauze; O, a disk of paper closely perforated with a largenumber of minute apertures, a. The piece of one or another material isplaced between layers of carbon, and the whole is pressed into anintegral structure, as above set forth.

The carbon b, covering the fabric and filling its interstices, is shownin an exaggerated manner in Fig. 5, and the complete carbon button D isseen in Fig. 4.

In my Patent No. 203,015, of April 30', 1878, is set forth a carbonelectrode composed of a number of fibers, each separately covered withcarbon and all rolled into a wad or tuft. My present invention, however,provides a better construction,inasmuch as it producesa flat button,which is more convenient in use and can be substituted in any ordinarytele phone for the usual carbon button, and does not require a bindingto hold it together. The present method of manufacture also is much moresimple and economical than that required to produce the article setforth in the patent referred to.

What I claim is 1. An electrode for a telephone-transmitter, consistingof a flat piece of textile fabric, or

equivalent, impregnated and covered with lamp-black, substantially asset forth.

5. The method herein described of forming an electrode for atelephone-transmitter, consisting in placing a piece of textile fabricbetween layers of carbon and pressing the whole together. V

This specification signed and witnessed this 12th day of January, 1885.

THOS. A. EDISON.

Witnesses:

A. W. KIDDLE, E. C. ROWLAND.

